The present invention relates to modifications of poly(acrylic acid) or polyacrylate, and in particular to a polysiloxaneurethane-poly(acrylic acid)/polyacrylate copolymer containing polysiloxane-urethane groups as a sidechain of the copolymer.
Acrylic resins commonly are designated as synthetic resins formed mainly from acrylic acid or acrylate compoundsl, for examples poly(acrylic acid), polyacrylate, polymethacrylic acid, polymethacrylate, and polyacrylonitrile. Generally speaking, acrylic resins have the following characteristics:
Colorless and transparent;
Capable of being freely colored by a dye;
Good surface glossiness;
Good weather resistance;
Excellent mechanical processability;
Excellent chemical resistance; and
Non-toxic to human body.
Although acrylic resins have the above-mentioned characteristics, their defects, such as brittleness and poor heat resistance, etc., severely limit the applications thereof. Therefore, currently acrylic resins mainly are used in adhesives, coatings, automobile parts, lighting utensils, and general building materials, etc., which have a low unit price, as well as a low value added. If these defects can be improved, the improved acrylic resins will have a broader range of applications, as well as an increased value added for the products made thereof.
The present invention firstly prepares a polysiloxane having an isocyanate group on the two ends thereof; which is then simultaneously reacts with an end capping compound and an acrylic acid or acrylate compound having a hydroxyl group, so that a macromonomer of polysiloxane-urethane having an unsaturated group of acrylic acid/acrylate compound at one end thereof is formed. An acrylic acid/acrylate monomer is added to the resulting reaction mixture to under free radical polymerization, so as to produce a polysiloxaneurethane-poly(acrylic acid)/acrylate copolymer.
A polysiloxaneurethane-poly(acrylic acid)/acrylate copolymer synthesized according to the present invention has a chemical structure as follows: 
wherein:
R1, R2 and R3 independently are hydrogen or C1-C4 alkyl;
nxe2x80x2=1-6; and 
xe2x80x83wherein:
(x+xxe2x80x2):(y+yxe2x80x2)=13:1 to 40:1;
R4 is 
R5 is C1-C6 alkylene;
R8 and R7 independently are C1-C4 alkyl;
R8 is C1-C4 alkoxyl or C2-C4 secondary amine; and
nxe2x80x2, R1 and R2 are defined as above.
Preferably, Q in the copolymer at least one Q is Q1 and at least one Q is Q2, and the ratio of Q1 and Q2 enables the copolymer having a swelling ratio of 2-7 after being immersed in tetrahydrofuran for a week.
Preferably, R4 is 
The present invention also discloses a method for preparing the polysiloxaneurethane-poly(acrylic acid)/acrylate copolymer comprising the following steps:
a) reacting a diisocyanate with a polysiloxane having two hydroxyl groups on its two ends at an equivalent ratio of 2:1 to 2.3:1 to prepare a NCO-terminated polysiloxane having each of its two ends terminated with an isocyanate group;
b) simultaneously reacting said NCO-terminated polysiloxane with an endcapping compound and an acrylic acid or acrylate compound containing a hydroxyl group to form a reaction mixture consisting essentially of a polysiloxaneurethane macromonomer having an acrylic acid/acrylate group on one end and a residue of the end-capping compound on the other end; said reaction mixture further comprising a small amount of a macromonomer having an acrylic acid/acrylate group on each of the two ends thereof, wherein the equivalent ratio of said NCO-terminated polysiloxane: said acrylic acid/acrylate compound having a hydroxyl group : said end-capping compound is 1:0.4:0.6 to 1:0.6:0.4; and
c) undergoing a free radical copolymerization in said reaction mixture after an acrylic acid/acrylate monomer being added to said reaction mixture.